Digital point spread function (DPSF) and dual modulation projection (including lasers) using DPSF

ABSTRACT

A digital PSF for use in a dual modulation display. The invention allows the use of less than optimal point spread (PSF) functions in the optics between the pre-modulator and primary modulator of a dual modulation projection system. This technique uses multiple halftones per frame in the pre-modulator synchronized with a modified bit sequence in the primary modulator to produce a compensation image that reduces the errors produced by the sub-optimal PSF. The invention includes the application to dual modulation and dual modulated 3D viewing systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/266,240 filed on Apr. 20, 2014, which claims benefit of priority ofU.S. Provisional Patent Application No. 61/820,683 filed on May 7, 2013entitled “Digital Point Spread Function (DPSF) and Dual ModulationProjection (including Lasers) using DPSF”; wherein the disclosure ofreference is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to display devices and more particularlyto dual modulation projectors (including laser projectors) and thecreation and use of a point spread function between modulators.

Discussion of Background

Dual modulation projectors and displays include display devices (e.g.,Whitehead U.S. Pat. No. 7,403,332, and Daly U.S. Pat. No. 7,064,740) andprojectors (e.g., Sayag U.S. Pat. No. 7,002,533).

SUMMARY OF THE INVENTION

The present inventor has realized the need to increase contrast andbrightness of projection displays and to reduce artifacts. The presentinvention includes generation of a digital PSF. The digital PSF may be,for example, a digital PSF of a modulated light source to illuminate amodulator of a projector or other display. The illuminated modulator maybe, for example, a primary (or final) modulator of a dual modulationprojection system, an intermediary modulator of a multi-modulationsystem, or, alternatively, any other modulator within a projection ordisplay system.

The digital PSF provides, for example, a PSF of any of a pixel, tile, orother area of a pre-modulator image or other lighting illuminating theprimary (or other) modulator that is configurable to account forvariations, discontinuities, abberations, or other non-uniformities in alight path between the pre-modulator and primary modulator such that auniform PSF is exhibited at the primary modulator. The digital PSF maybe utilized to assure a consistent PSF among all pixels (or any group ofpixels) in an image, image path, or as illuminated on the primarymodulator.

In one embodiment, the present invention provides a dual modulationprojector containing a pre modulator, relay optics, and a primarymodulator, and where pre-compensation for imperfections of the relayoptics PSF is made by modifying the image sent to the pre modulator(pre-modulator image). The result is a desired uniformity and/or shapeof the light illuminating the primary modulator.

The desired uniformity and/or shape of the light illuminating theprimary modulator may be different for different portions of the image.The pre-compensation may be a filter that is different for differentregions of the image. The resulting PSF of pixels of the lightilluminating the primary modulator may be flatter in areas of the imagehaving predominately lower spatial frequencies, and the resulting PSF ofpixels of the light illuminating the primary modulator may be sharper inareas of the image having predominately higher spatial frequencies. ThePSFs may be different based on wavelengths of light being modulated. Inone embodiment, all PSFs in a region of the image have similarly shapedPSFs when illuminating a corresponding area of the primary modulator.The shapes of the same lights may be different before transfer optics orother optical elements in the light path between modulators, thedifferences being pre-compensation that adjusts the light to account forhow the different lights change en-route to the primary modulator.Ideally, the compensation is different for each wavelength of lightwhich reacts differently to different optical elements within the lightpath.

The pre-compensation filter may include coefficients are calculatedbased upon PSF measurements and a reference desired PSF.

Additional compensation is made by the primary modulator. The additionalcompensation includes, for example, compensation to further modulate thelight illuminating the primary modulator into the desired image. Theadditional compensation may also include compensation for a PSF of oneor more pixels.

The pre-modulator may be, for example, a DMD “displaying” a halftoneimage. The primary modulator may also be a DMD. The invention may beimplemented on combinations of reflective and transmissive modulatorswith any of polarizers, reflectors, dichroics, PBSs, or other opticalelements as relay optics between the modulators. The pre-modulatoritself may be illuminated by any combination of broadband light sources,narrowband light sources, modulated light sources. Preferably, thepre-modulator is illuminated by a laser light source that is at leastglobally dimmed and may include some form of local dimming (or spatialmodulation) to further increase contrast.

The invention includes a half-tone or other image on a pre-modulatorthat is changed multiple times per frame, and where bit sequences thatenergize the pre-modulator for each of those multiple times per frameare synchronized with corresponding energization signals of the primarymodulator. The invention includes a pre-modulator DMD energized with ahalftone image and a primary modulator DMD. The pre-modulator'shalf-tone image is changed multiple times per frame, and where the bitsequences on the pre-modulator DMD the primary modulator DMD aresynchronized, such that an average across the frame is the product of anaverage of the pre-modulator images through the relay optics and theprimary modulator image. In various embodiments, the pre-modulator halftone image is changed any of twice, three times, four times, and eighttimes or more per frame. The number of times per frame that thepre-modulator image may change may be variable, such that, for example,for some frames the pre-modulator image is changed twice per frame, andfor other frames it is changed 4 times per frame. The number ofpre-modulator half-tone changes may be updated when transitioningbetween 2D and 3D projection modes or transitioning between single anddual projector modes, or utilizing additional projectors. The number ofhalftone changes may be changed when transitioning between differentenvironments. The number of half tone changes may be different fordifferent projectors and/or similar projectors in differentenvironments, for example when displaying cinema content to riders in atheme park ride as they transition from scene to scene in differentportions of the ride that may utilize different projectors or aplurality of similar projectors in different environments.

The DMDs are synchronized such that the average across the frame is theproduct of the average of the pre-modulator images through the relayoptics and the primary modulator image.

In one embodiment, the pre-modulator half-tone image is changed three ormore times per frame and in synchronization with the final modulatorimage that is changed at least once per frame.

-   -   1) The present invention includes a method of energizing a        pre-modulator, comprising the steps of: Obtaining a 2D PSF of        relay optics or other non-uniformities in a light path between        the pre-modulator and a primary modulator;    -   2) Calculating a correction factor comprising difference between        a desired PSF and the 2D PSF;    -   3) Applying the correction factor to a pre-modulator image; and    -   4) Energizing the pre-modulator with the corrected pre-modulator        image.

The invention allows the use of less than optimal point spread (PSF)functions in the optics between the pre-modulator and primary modulatorof a dual modulation projection system. This technique uses multiplehalftones per frame in the premodulator synchronized with a modified bitsequence in the primary modulator to produce a compensation image thatreduces the errors produced by the sub-optimal PSF.

Portions of the invention may be conveniently implemented in programmingon a general purpose computer, or networked computers, and the resultsmay be displayed on an output device connected to any of the generalpurpose, networked computers, or transmitted to a remote device foroutput or display. In addition, any components of the present inventionrepresented in a computer program, data sequences, and/or controlsignals may be embodied as an electronic signal broadcast (ortransmitted) at any frequency in any medium including, but not limitedto, wireless broadcasts (satellite, Wi-Fi, WI-Max, etc.), andtransmissions over copper wire(s), fiber optic cable(s), and co-axcable(s), etc.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an illustration of an example PSF and a corrected PSF; and

FIG. 2 is a diagram of an example bit sequence.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The current dual modulation POC EDR projector uses a single half toneimage per frame on the pre-modulator. A problem arises when the PSF ofthe relay optics between the two modulators is sub optimal, especiallywhen the resultant PSF is multi-lobed, or non-monotonic in anydirection. In order to compensate for sub-optimal PSFs with a singlehalftone image, the compensation is performed in the primary modulator.This can be done if the PSFs are reasonably well controlled across theframe and with the use of multiple PSFs within the dual modulationalgorithm, and interpolation between PSFs across the frame. Ultimately,one could use a different PSF for every pixel within the frame, but thiswould create additional computation burden. In addition, theregistration between the two modulators should be precise, and there aresome limitations due to the limited contrast ratio of the primarymodulator. Also, measurement or alignment errors may show up as highspatial frequency errors in the final image.

FIG. 1 provides examples of PSFs from the relay optics. The left PSF 110is sub-optimal, while the right PSF 120 is desirable. As can be seen inFIG. 1, sub-optimal PSF 110 includes a less predictable clover-leaf likepattern 115, and desirable PSF 125 is rounded and fades in a moreconsistent or controlled/predictable manner.

It would be better if the apparent PSF at the primary modulator was wellcontrolled. One way of obtaining this is to average over several PSFs.As a practical matter, a single pixel turned on in the halftone image ofthe pre-modulator produces a small enough point to produce a pointspread function on the primary modulator; thus the PSF can be measuredon the projected image by turning the primary modulator to all white inthe presence of single ‘on’ pixels in the pre-modulator.

Normally, in a dual modulation system we are rarely if ever turning on asingle pixel in the pre-modulator, therefore multiple PSFs are typicallypresent. If the PSFs are significantly larger than the tile size (whichlimits the highest spatial frequency that can be obtained) of thehalftone image, one can obtain a PSF correction for the pre-modulatorimage which is used to generate the halftone image. The process may beimplemented as:

-   -   1. Obtain 2D PSF of relay optics and its 2D Fourier Transform.        rpsf(x,y), RPSF(wx,wy).    -   2. Specify desired PSF dpsf(x,y), DPSF(wx,wy).    -   3. Calculate the correction factor        Zc(x,y)(wx,wy)=DPSF(wx,wy)/RPSF(wx,wy) for a large number of        regions in the image, and interpolate to obtain a smoothly        changing Zc as a function of x,y. Obtain inverse Fourier        Transform of Zc(x,y)(wx,wy)=zc(x,y)(x,y).    -   4. Apply Zc to each region of the premod image. This might be        best done in the location domain as Corrected Image CI=zc        convolved with the premod image.

These calculations determine a correction factor that filters thepremodulator image in such a way that when combined with the PSF of theoptics an image is produced where the inconsistencies of the optics PSFis smoothed to the desired psf. Of course, this only works if the relayoptics PSFs are larger than the smallest feature that can be obtainedfrom a halftone conversion of the premod image. This last point isimportant, as it limits the application of this approach to requiringlarge relay optics PSFs.

Addressing the halftone feature limitation requires an approach similarto that described in co-pending U.S. Patent Publication 2014/0333835. Inthis implementation, instead of increasing the number of levels for thehalftone image, we could use the same technique to decrease the size ofthe halftone tiles, so that the feature size was reduced.

As an example, let us assume that we originally had a 4×4 tile (16levels), and we now divide the picture frame into 4 sub-frames. The tilesize can now be reduced to 2×2 and still obtain 16 levels. The featureresolution in the halftone image has doubled, allowing smaller relayoptics PSFs to be compensated.

The amount of effort to compensate for the PSFs has not reduced from theoriginal design where all of the correction was done in the primarymodulator, however, this approach reduces the visibility of errorscaused by misalignment and measurement error verses the originalapproach using the primary modulator. These errors are translated intolow frequency type errors which have lower visibility.

As described in co-pending U.S. Patent Publication 2014/0333835, if aDMD (TI Digital Mirror Device) is used for the primary modulator,modification of the bit sequences for the modulation chips will berequired. The DMD uses a form of pulse width modulation to modulate thelight; therefore, the light is required to be constant during the entireframe period. Changing the pre-mod halftones during the frame (4 times)would produce a non-constant light, and interfere with the PWM result.

Normally the DMD is used with a single sequence per frame to obtain a 16bit per pixel modulation. It is proposed to modify the bit sequence sothat the higher order bits are spread across the frame period;therefore, they are repeated multiple times. For example, if the top 14bits (of 16) are repeated, this would allow a pattern with the top 14bits repeated 4 times. The lower significant bits would remainunaffected, (spread across the entire frame period). This type ofrepeated sequencing has been described in the literature and is used toreduce motion artifacts with DMD based projection systems. U.S. Pat. No.5,986,640 describes a similar technique. The halftone image on thepre-modulator would be synchronized with the repeated sequences in theprimary modulator such that both modulators would change to a newsequence at the same time.

A proposed sequence that could operate under the requirements of thepresent invention is illustrated in FIG. 2.

The single sequence illustrates a standard half-tone only modulatorsequence for a single frame. The double sequence illustrates the singlesequence divided into two partitions for the frame. The quad sequenceillustrates the single sequence divided into four partitions for theframe. More specifically, as shown in FIG. 2, the proposed sequenceprovides an example single sequence 210 illustration for a half-toneonly modulator sequence for a single frame (e.g., frame period 240). Adouble sequence 229 illustrates the single sequence divided into twopartitions for the frame. A quad sequence 230 illustrates the singlesequence divided into four partitions for the frame (partitions dividedat 252, 245, and 254, for example).

The divided sequences are, for example, provided different bit sequencesrepresenting different half-tone images applied to the same frame (and,for example, the same primary modulator image). The divided sequencesmay alternate between a first and second half-tone image. The dividedsequences may implement a rotating sequential application of first,second, and third half-tone images for each frame. The half-tone imagesimplemented for each frame include, for example, compensation of relayoptics or other variations as described above. Based on the abovedisclosure, many other sequences may be developed, customized,synchronized or chained together to perform the same result, any one ormore of which may be implemented together or separately in conjunctionwith any other aspect (or aspects) of the present invention.

The pre-modulator is preferably illuminated by laser light sources andthe compensation of the pre-modulator image preferably compensates forwavelength specific aspects of the relay optics. Preferably, the resultis a PSF of each pixel (or groups of pixels) for each of the half-toneimages that are similarly shaped and varying smoothly from one-pixel tothe next. The shapes of the PSFs in groups of pixels in regions of theimage being modulated are the same or similar and any differencesbetween PSFs of neighboring regions may, preferably, smoothly transitionfrom the first region's preferred PSF to the adjoining region'spreferred PSF. For 3D projections, the pre-modulator image iscompensated to account for wavelength differences and associatedwavelength dependent PSF changes between different colors (or differentwavelengths) of the same or different viewing channels (e.g., leftand/or right eye viewing channels), and/or similar differences/changesin the same colors (different wavelengths) of different or same viewingchannels.

In various embodiments, the present invention may be a dual modulationprojector containing a pre modulator, relay optics, and a primarymodulator, and where pre-compensation for imperfections of the relayoptics PSF is made by modifying the image sent to the pre modulator. Thepre-compensation filter is different for different regions of the image.The pre-compensation filter coefficients may be calculated based uponPSF measurements and a reference desired PSF. Additional compensation ismade in the primary modulator. The pre-modulator image may be a halftoneimage on a DMD, and the primary modulator may be a DMD. The halftoneimage may be changed multiple times per frame, and where the bitsequences on the pre-modulator DMD and primary modulator DMD aresynchronized, such that the average across the frame is the product ofthe average of the pre-modulator images through the relay optics and theprimary modulator image.

The present invention may comprise a projector comprising apre-modulator to modulate light into a first image, a primary modulatorconfigured to further modulate the light to produce a desired image, andrelay optics configured to transfer the modulated light of the firstimage to the primary modulator, wherein the transfer optics are furtherconfigured to spread pixels of the first image so that each pixel of thefirst image illuminates a plurality of pixels of the primary modulator.The invention may further comprise a controller configured to energizethe first modulator with a backlight image based on image data of thedesired image, the backlight image further comprising an adjustment ofpixels of the backlight image to compensate for non-uniformity on theprimary modulator of one or more of the first image pixels. Thecompensation may comprise a difference between a desired point spreadfunction of light transferred from the pre-modulator to the primarymodulator and a PSF and/or MTF of the relay optics. The backlight (orpre-modulator) image comprises a convolution of a low resolution versionof the desired image and the difference. The compensation may comprise acompensation scheme selected from a plurality of compensation schemesbased on the desired image. The compensation may comprise a non-linearequation adjusted based on the desired image. The compensation maycomprise a compensation scheme selected or derived based on a spatialfrequency parameter of the image and a wavelength of light beingmodulated. The compensation may comprise one or a combination of aplurality of compensation schemes applied to different portions of thebacklight image.

A projector according to the invention may comprise a multi-colorchannel projector each channel comprising a similar configuration of apre-modulator, primary modulator, and transfer optics, said controllerenergizing each pre-modulator with image data comprising a backlightimage for each color channel along with a color specific compensation.The compensation may comprise an inverse of a non-uniformity ofspreading of pixels of the pre-modulator onto multiple pixels of theprimary modulator according to wavelengths of light modulated in eachchannel. The first modulator may comprise one of a transmissivemodulator and a reflective modulator, and the primary modulatorcomprises one of a transmissive modulator and a reflective modulator,and the first modulator and second modulator are not necessarily thesame type of modulator.

Projectors according to the present invention may comprise modulators ofdifferent types or the pre-modulator and primary modulators are both DMDmodulators. The pre-modulator and primary modulators may beLiquid-Crystal-on-Silicon (LCoS) modulators. Any of the projectors maybe configured for projecting 3D images such as wherein the pre-modulatorimages comprise 1st and 2nd channel images of a 3D image, and thepre-modulator may be energized by compensated pre-modulator imagescomprising left and right images of a 3D image, and wherein theprojector is part of a system for displaying an viewing 3D imagescomprising glasses comprising filters corresponding to the left andright images comprising filter passbands encompassing wavelengths of theleft and right images.

In the 3D embodiments, the wavelengths of the left image may originate,for example, from a laser light source illuminating a pre-modulatorwhile being energized with a compensated pre-modulator left imagecorresponding the illuminating wavelengths in a left image time frame;wavelengths of the right image originate from a laser light sourceilluminating the pre-modulator while being energized with a compensatedpre-modulator right image corresponding to the illuminating wavelengthsin a right image time frame.

The projectors of the present invention in multi-view and/or 3Dembodiments may be, for example, part of a system for displaying andviewing 3D images and the modulated desired images are passed viawavelength selective filters in 3D viewing glasses such that modulatedwavelengths of the left images of the 3D images are passed by a leftfilter of the 3D viewing glasses and modulated wavelengths of the rightimages of the 3D images are passed by a right filter of the 3D viewingglasses and the filters comprise passbands that are offset relative tothe wavelengths being viewed through the passbands such that wavelengthsof the compensated half-tone images further modulated into desired leftand right images by the primary modulator are passed via passbands thatencompass and are shifted toward longer wavelengths compared to thewavelengths of the intended image wavelengths passed through thepassbands. Such arrangement allow for capturing laser wavelengths partof compensated half-tone images further modulated for viewing at obliqueangles.

Although the present invention has been described herein with referenceto DMDs and dual modulation systems, the devices and processes of thepresent invention may be applied to other modulation types andmulti-modulation architectures.

In describing preferred embodiments of the present invention illustratedin the drawings, specific terminology is employed for the sake ofclarity. However, the present invention is not intended to be limited tothe specific terminology so selected, and it is to be understood thateach specific element includes all technical equivalents which operatein a similar manner. For example, when describing a lens, modulators,relay optics, etc., any other equivalent device, or other device havingan equivalent function or capability, whether or not listed herein, maybe substituted therewith. Furthermore, the inventors recognize thatnewly developed technologies not now known may also be substituted forthe described parts and still not depart from the scope of the presentinvention. All other described items, including, but not limited tomodulators, projectors, data processing, etc should also be consideredin light of any and all available equivalents.

Portions of the present invention may be conveniently implemented usinga conventional general purpose or a specialized digital computer ormicroprocessor programmed according to the teachings of the presentdisclosure, as will be apparent to those skilled in the computer art.

Appropriate software coding can readily be prepared by skilledprogrammers based on the teachings of the present disclosure, as will beapparent to those skilled in the software art. The invention may also beimplemented by the preparation of application specific integratedcircuits or by interconnecting an appropriate network of conventionalcomponent circuits, as will be readily apparent to those skilled in theart based on the present disclosure.

The present invention includes a computer program product which is astorage medium (media) having instructions stored thereon/in which canbe used to control, or cause, a computer to perform any of the processesof the present invention. The storage medium can include, but is notlimited to, any type of disk including floppy disks, mini disks (MD's),optical discs, DVD, CD-ROMS, CD or DVD RW+/−, micro-drive, andmagneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, DRAMs, VRAMs, flashmemory devices (including flash cards, memory sticks), magnetic oroptical cards, SIM cards, MEMS, nanosystems (including molecular memoryICs), RAID devices, remote data storage/archive/warehousing, or any typeof media or device suitable for storing instructions and/or data.

Stored on any one of the computer readable medium (media), the presentinvention includes software for controlling both the hardware of thegeneral purpose/specialized computer or microprocessor, and for enablingthe computer or microprocessor to interact with a human user or othermechanism utilizing the results of the present invention. Such softwaremay include, but is not limited to, device drivers, operating systems,and user applications. Ultimately, such computer readable media furtherincludes software for performing the present invention, as describedabove.

Included in the programming (software) of the general/specializedcomputer or microprocessor are software modules for implementing theteachings of the present invention, including, but not limited to,calculating PSFs, adjusting PSFs by any of addition, subtraction,multiplication, and convolution; energizing modulators with half-tonedata and synchronizing half-tome data as energized with energizations ofother modulators in a same optical path, and the display, storage, orcommunication of results according to the processes of the presentinvention.

The present invention may suitably comprise, consist of, or consistessentially of, any of element (the various parts or features of theinvention and their equivalents as described herein. Further, thepresent invention illustratively disclosed herein may be practiced inthe absence of any element, whether or not specifically disclosedherein. Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A projector comprising: a pre-modulator configuredto modulate light into a first image; a primary modulator configured tofurther modulate the light to produce a desired image; one or more relayoptics configured to transfer the modulated light of the first image tothe primary modulator, wherein the transfer optics are furtherconfigured to spread pixels of the first image so that each pixel of thefirst image illuminates a plurality of pixels of the primary modulator;and a controller configured to energize the pre-modulator with abacklight image based on image data of the desired image, the backlightimage further comprising an adjustment of pixels of the backlight imageto compensate for imperfections of the relay optics; wherein thecompensation comprises a difference between a desired point spreadfunction (PSF) of light transferred from the pre-modulator to theprimary modulator and a PSF of the relay optics.
 2. The projectoraccording to claim 1, wherein the backlight image comprises aconvolution of a low-resolution version of the desired image and thedifference.
 3. The projector according to claim 1, wherein thecompensation comprises a compensation scheme selected from a pluralityof compensation schemes based on the desired image.
 4. The projectoraccording to claim 1, wherein the compensation comprises a non-linearequation application adjusted based on the desired image.
 5. Theprojector according to claim 1, wherein the compensation comprises acompensation scheme selected or derived based on a spatial frequencyparameter of the image and a wavelength of light being modulated.
 6. Theprojector according to claim 1, wherein the compensation comprises aplurality of compensation schemes applied to different portions of thebacklight image.
 7. The projector according to claim 1, wherein theprojector comprises a multi-color channel projector each channelcomprising a similar configuration of a pre-modulator, primarymodulator, and relay optics, and said controller energizing eachpre-modulator with image data comprising a backlight image of each colorchannel along with a color specific compensation.
 8. The projectoraccording to claim 7, wherein the compensation comprises an inverse of anon-uniformity of spreading of pixels of the pre-modulator onto multiplepixels of the primary modulator according to wavelengths of lightmodulated in each channel.
 9. The projector according to claim 6,wherein the pre-modulator comprises one of a transmissive modulator anda reflective modulator, and the primary modulator comprises one of atransmissive modulator and a reflective modulator.
 10. The projectoraccording to claim 1, wherein the pre-modulator and primary modulatorsare digital micromirror device (DMD) modulators or liquid crystal onsilicon (LCoS) modulators.
 11. The projector according to claim 1,wherein the pre-modulator is energized by compensated pre-modulatorimages comprising left and right images of a 3D image, and wherein theprojector is part of a system for displaying an viewing 3D imagescomprising glasses comprising filters corresponding to the left andright images comprising filter passbands encompassing wavelengths of theleft and right images.
 12. The projector according to claim 11, whereinwavelengths of the left image originate from a laser light sourceilluminating a pre-modulator while being energized with a compensatedpre-modulator left image corresponding the illuminating wavelengths in aleft image time frame; wavelengths of the right image originate from alaser light source illuminating the pre-modulator while being energizedwith a compensated pre-modulator right image corresponding to theilluminating wavelengths in a right image time frame.
 13. The projectoraccording to claim 12, wherein the projector is part of a system fordisplaying and viewing 3D images and the modulated desired images arepassed via wavelength selective filters in 3D viewing glasses such thatmodulated wavelengths of the left images of the 3D images are passed bya left filter of the 3D viewing glasses and modulated wavelengths of theright images of the 3D images are passed by a right filter of the 3Dviewing glasses and the filters comprise passbands that are offsetrelative to the wavelengths being viewed through the passbands such thatwavelengths of compensated half-tone images further modulated intodesired left and right images by the primary modulator are passed viapassbands that encompass and are shifted toward longer wavelengthscompared to the wavelengths of the intended image wavelengths passedthrough the passbands.